A light emitting device includes a P-N junction diode having a characteristic of converting electrical energy into light energy. The light emitting device may be produced using compound semiconductors belonging to group III and V on the periodic table. The light emitting device can represent various colors by adjusting the composition ratio of the compound semiconductors.
When forward voltage is applied to the light emitting device, electrons of an N layer are combined with holes of a P layer, so that energy may be diverged corresponding to band gap energy between a conduction band and a valance band. The energy is mainly emitted in the form of heat or light. In the case of the light emitting device, the energy is diverged in the form of light.
For example, a nitride semiconductor represents high thermal stability and wide band gap energy so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and ultraviolet (UV) light emitting devices employing the nitride semiconductor have already been commercialized and extensively used.
In particular, as the UV light emitting device is increasingly utilized, the demand for the UV light emitting device is increased, so that the interest in the UF light emitting device is raised.
However, a light emitting structure of the UV light emitting device may be formed of a material having compositions different from those of other nitride light emitting devices. Accordingly, when other structures (for example, a dislocation control layer, a strain control layer, a current spreading layer, and the like) provided in a light emitting device to emit lights of different light emitting bands are applied to the UV light emitting device except for the light emitting structure, the UV light emitting device may produce an unexpected adverse effect instead of the effects of other nitride light emitting devices.
Meanwhile, a light emitting device may be classified into a lateral type and a vertical type according to the positions of an electrode.
According to the vertical type of the light emitting device of the related art, when a growth substrate is removed and the electrode is connected, operating voltage (VF) may be affected or light loss (Po) may be caused according to the compositions of a semiconductor layer making contact with the electrode.
Meanwhile, according to a light emitting device having a conventional structure, if a quantity of injected current is increased, light emission efficiency may be degraded because hole injection efficiency is lower than electron injection efficiency in a light emission layer. In order to solve the above problem, there is required the development of a technology that holes can be effectively moved from a p layer to an n layer in the light emission layer, so that the holes can be uniformly distributed in the light emission layer, thereby allowing all quantum wells of the light emission layer to participate in light emission.